1. Field of the Invention
This invention relates to a sliding type or plunging type constant velocity universal joint, and more particularly to a plunging type tripod universal joint suitably incorporated in a drive shaft or the like of a vehicle.
2. Description of the Prior Art
A plunging type tripod universal joint comprises an outside member connected to a first shaft and provided on the inner peripheral surface with three grooves extending in an axial direction of the first shaft at circumferentially equal intervals, an inside member connected to a second shaft and having tripod shafts extending outward in a radial direction of the second shaft so as to respectively enter into the grooves, and a ring-like roller rotatably supported by each tripod shaft and contacting with the outside member.
When the constant velocity universal joint as mentioned above is rotated under the condition that the axes of the first and second shafts cross each other, that is, the first and second shafts make a joint angle to each other, a forced force or axial excitation of the period which is three times larger than the rotational frequency, i.e., a so-called periodic axial force, is generated in the axial direction of the shaft to vibrate a vehicle. As shown in FIG. 17, the axial excitation is generated by a rolling component A resulting from the rolling friction between a roller 20 and a roller groove 21, a spin component B resulting from spin and a sliding component C resulting from the sliding friction between the tripod shaft or the cage and the inner peripheral surface of the roller and the sliding friction between the outer peripheral surface of the roller and the roller groove.
The above-mentioned three components do not uniformly contribute to the generation of the axial excitation. As shown in FIG. 19, the sliding component C has the largest influence on the generation of the axial excitation according to calculation. As shown in FIG. 18, since portions of contact of the roller 20 with the roller groove 21 are always located on a normal plane of an axis of an outside member 22, the sliding component C is mainly based on the fact that the direction of a frictional force f is deflected from a reaction component F.sub.1 of a drive force F by an angle .theta. to generate a residual component f.sub.1 of the frictional force f.
While there have been many proposals for reducing the axial excitation, the proposals related to the present invention are disclosed in Japanese Patent Public Disclosures (KOKAI) No. 1-288626, No. 63-158327 and No. 54-132046 and Japanese Utility Model Public Disclosure (KOKAI) No. 64-6425.
According to a constant velocity universal joint disclosed in the reference 1-288626, a roller is composed of an inner ring, an intermediate ring and an outer ring. The inner ring of the roller is mounted on a tripod shaft through a needle bearing such that the rotation alone of the inner ring is possible. The outer periphery of the inner ring of the roller is formed into a spherical surface having the center on an axis of the tripod shaft. The spherical surface of the inner ring of the roller is brought into spherical contact with the inner periphery of the intermediate ring of the roller, and the outer periphery of the intermediate ring of the roller is formed into a cylindrical surface along an axis of the intermediate ring of the roller, so that the inner periphery of the outer ring of the roller is fitted to the cylindrical surface of the intermediate ring of the roller.
According to a constant velocity universal joint disclosed in the reference 64-6425, an inside roller is slidably fitted to a tripod shaft. The outer periphery of the inside roller is formed into a convex spherical surface having the center on an axis of the tripod shaft. A holder having a concave spherical surface adapted for fitting to the convex spherical surface of the inside roller is swingably fitted to the inside roller, and an outside roller is rotatably mounted on the holder. The holder is provided with a flange for restraining the inclination of the holder.
According to a constant velocity universal joint disclosed in the reference 63-158327, a roller is composed of an outer ring provided on the outer periphery with a cylindrical surface, an inner ring fitted to a tripod shaft and a plurality of needle rollers disposed between the outer ring and the inner ring. The outer periphery of the tripod shaft is formed into a convex spherical surface having the center on an axis of the tripod shaft, and the inner ring has a concave spherical surface adapted for fitting to the convex spherical surface of the tripod shaft. In this universal joint, two groove surfaces of a groove on an outside member for inserting the tripod shaft are formed as parallel planes, and the outer ring rolls on these parallel planes. The outer ring is swingable in a plane parallel to the plane including the axes of three tripod shafts.
According to a constant velocity universal joint disclosed in the reference 54-132046, a tripod shaft or a guide ring mounted on the tripod shaft is provided with a convex spherical surface having the center on an axis of the tripod shaft, and an concave spherical surface of a cage is fitted to the convex spherical surface to permit a roller to swing relative to the tripod shaft.
In order to reduce the above-mentioned periodic axial force, it is most effective to reduce the sliding component. In this connection, when two shafts are rotated with the joint angle made between the two shafts, it is preferable to eliminate the residual component of the frictional force as mentioned above by maintaining the positions of all parts between the tripod shaft and the outside member, i.e., the roller, the needle rollers, the cage or the like relative to the axis of the outside member constant such that the sliding frictional force among the parts is generated on the normal plane to the axis of the outside member.
In the constant velocity universal joint disclosed in the reference 1-288626, when the two shafts are rotated with the joint angle made between the two shafts, the inner ring of the roller united with the tripod shaft by a snap ring slides on the intermediate ring of the roller through their spherical surfaces, and the intermediate ring of the roller slides on the outer ring of the roller in the axial direction of the intermediate ring of the roller. As a result, the positions of the outer ring and the intermediate ring of the roller relative to the roller groove are maintained constant. Since the intermediate ring of the roller is moved relative to the outer ring of the roller in the radial direction orthogonal to the axis of the outside member, the sliding component as mentioned above is reduced. On the other hand, since the position of the inner ring of the roller is not maintained constant relative to the axis of the outside member, the needle rollers disposed between the tripod shaft and the inner ring of the roller are inclined due to the inclination of the tripod shaft, so that the needle rollers do not fulfill their inherent function to the rotation of the outer ring of the roller. Therefore, the sliding surface during the rotation of the outer ring of the roller is not defined, and besides, the surfaces of the sliding portions make contact with each other. As a result, in the universal joint, the sliding component is reduced, while the sliding friction is included in the rolling component.
In the constant velocity universal joint disclosed in the reference 64-6425, when the two shafts are rotated with the joint angle made between the two shafts, the tripod shaft swings together with the inside roller, while the inclination of the holder is restrained by the flange. As a result, the position of the outside roller relative to the roller groove is maintained constant. On the other hand, the tripod shaft is moved relative to the inside roller in the axial direction of the tripod shaft, so that the residual component of the sliding frictional force results in the axial excitation.
In the constant velocity universal joint disclosed in the reference 63-158327, the parts between the tripod shaft and the outer ring are substantially united, and it is intended that the sliding frictional force is not generated. However, in the rotation of the tripod universal joint with the joint angle, an output shaft always oscillates three times per one rotation, and the oscillations of the output shaft are absorbed by the spherical surface contact of a spherical bushing with the inner ring and the sliding movement between the outer ring and the outside member. The residual component of the sliding frictional force generated between the outer ring and the outside member results in the axial excitation, since the position of the outer ring is not constant relative to the axis of the outside member.
In the constant velocity universal joint disclosed in the reference 54-132046, when the two shafts are rotated with the joint angle made between the two shafts, the roller is actually inclined together with the cage, since nothing regulates the inclination of the roller. As a result, the sliding component is generated, or when the inclination of the roller is regulated, the axial excitation is generated by the sliding frictional force, similarly to the case of the universal joint disclosed in the above-mentioned reference 64-6425.